Steering mechanism for bi-directional catheter

ABSTRACT

The present invention provides a bi-directional catheter with nearly double the throw in its catheter tip deflection. In particular, the travel path of each the puller wire includes a U-turn or doubling-back around a pulley which minimizes the offset angle between the puller wire and the longitudinal axis of the control handle while maximizing the travel distance of that puller wire for any given distance traveled by the pulley drawing the puller wire. In one embodiment, the catheter has an elongated catheter body, a catheter tip section with first and second diametrically-opposed off-axis lumens, and a control handle which includes a steering assembly having a lever structure carrying a pair of pulleys for simultaneously drawing and releasing corresponding puller wires to deflect the tip section of the catheter.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.12/127,704 filed May 27, 2008, which is a continuation of U.S.application Ser. No. 10/871,691, filed Jun. 15, 2004 which issued asU.S. Pat. No. 7,377,906 on May 27, 2008, the entire contents of all ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to improved bidirectional steerablecatheters, and more particularly to a catheter having a bidirectionalcontrol handle.

BACKGROUND OF THE INVENTION

Electrode catheters have been in common use in medical practice for manyyears. They are used to stimulate and map electrical activity in theheart and to ablate sites of aberrant electrical activity. In use, theelectrode catheter is inserted into a major vein or artery, e.g.,femoral artery, and then guided into the chamber of the heart which isof concern. Within the heart, the ability to control the exact positionand orientation of the catheter tip is critical and largely determineshow useful the catheter is.

Bidirectional catheters have been designed to be deflectable in onedirection by one puller wire and in the opposite direction within thesame plane by a second puller wire. In such a construction, the pullerwires extend into opposing off-axis lumens within the tip section of thecatheter. So that the tip section can bend in both directions in thesame plane, the puller wires and their associated lumens must be locatedalong a diameter of the tip section. For ablation catheters, electrodelead wires must also be provided within the distal end. Typically, anadditional lumen is used to contain the electrode lead wires. Forexample, U.S. Pat. No. 6,210,407, the disclosure of which isincorporated herein by reference, is directed to a bi-directionalcatheter comprising two puller wires and a control handle having atleast two moveable members longitudinally movable between first andsecond positions. The proximal end of each puller wire is connected toan associated movable member of the control handle. Proximal movement ofa movable member relative to the catheter body results in proximalmovement of the puller wire associated with that movable member relativeto the catheter body, and thus deflection of the tip section in thedirection of the lumen in which that puller wire extends.

As another example, U.S. Pat. No. 6,171,277, the disclosure of which isincorporated herein by reference, is directed to a bidirectionalsteerable catheter having a control handle that houses agenerally-circular spur gear and a pair of spaced apart rack gears. Eachrack gear is longitudinally movable between first and second positions,whereby proximal movement of one rack gear results in rotationalmovement of the spur gear, and correspondingly distal movement of theother rack gear. Two puller wires extend from the control handle whosethe distal ends are fixedly attached to the tip section, and whoseproximal ends are each anchored to a separate associated rack gear inthe control handle. Proximal movement of a rack gear and its associatedpuller wire relative to the catheter body results in deflection of thetip section in the direction of the off axis lumen into which thatpuller wire extends.

Also known is U.S. Pat. No. 6,198,974, the disclosure of which isincorporated herein reference, is directed to a bi-directional electrodecatheter comprising a control handle. At their proximal ends, two pairsof puller wires are attached to movable pistons in the control handle.Each piston is controlled by an operator using a slidable button fixedlyattached to each piston. Movement of selected buttons results indeflection of the tip section into a generally planar “U”—or “S”-shapedcurve.

Further known is U.S. Pat. No. 5,891,088, the disclosure of which isincorporated, directed to a steering assembly with asymmetric left andright curve configurations. Proximal ends of left and right steeringwires are adjustably attached to a rotatable cam housed in a controlhandle. The rotatable cam has first and second cam surfaces which may beconfigured differently from each other to accomplish asymmetricsteering.

While the aforementioned catheters provide bi-directional steering, themechanical efficiencies of the steering or deflection mechanism can beimproved upon. Because the control handle has limited interior space inwhich to house the steering mechanism, a need exists for a compact yetmechanically-efficient design to accomplish bi-directional steering.Moreover, a greater degree of deflection in the catheter tip is alsodesirable, particularly if it can be accomplished without requiringgreater exertion on the part of the user. The steering assembly ofaforementioned U.S. Pat. No. 5,891,088 employs a configuration wherebythe puller wires extend to the cam surfaces of the rotatable cam at agreater than generally desirable angle from the longitudinal axis of thecatheter shaft, which decreases the efficiency of the steering lever andincreases friction losses in the operation of the steering assembly. Inaddition, the steering assembly therein generally limits the amount oflongitudinal movement of the puller wires for deflecting the cathetertip to only the circumference of the rotatable cam. An improved catheterwith bi-directional deflection is therefore desired.

SUMMARY OF THE INVENTION

The present invention provides a bi-directional catheter

with nearly double the throw in its catheter tip deflection. Inparticular, the travel path of each the puller wire includes a U-turn ordoubling-back around a pulley which minimizes the offset angle betweenthe puller wire and the longitudinal axis of the control handle whilemaximizing the travel distance of that puller wire for any givendistance traveled by the pulley drawing the puller wire.

In one embodiment, the catheter has an elongated catheter body, acatheter tip section with first and second diametrically-opposedoff-axis lumens, and a control handle which includes a steering assemblyhaving a lever structure carrying a pair of pulleys for simultaneouslydrawing and releasing corresponding puller wires to deflect the tipsection of the catheter. In particular, the pulleys are rotatablymounted on opposing portions of the lever structure such that one pulleyis moved distally as the other pulley is moved proximally when the leverstructure is rotated. Because each puller wire is trained on arespective pulley, rotation of the lever structure causes the pulleythat is moved proximally to draw its puller wire to deflect the tipsection in the direction of the off-axis lumen in which that puller wireextends.

In a detailed embodiment of the invention, each puller wire is trainedabout its respective pulley for about 180-187 degrees. Moreover, eachpuller wire may extend from the distal end of the control handle to itsrespective pulley at an angle no greater than about 10 degrees, or morepreferably between 7 and 8 degrees, from the longitudinal axis of thecontrol handle. Furthermore, the range of rotation of the leverstructure in deflecting the catheter tip can be predetermined through apredetermined profile or curvature in the housing of the control handle.

In another embodiment of the invention, the control handle of thecatheter includes a pair of constant force springs to draw up slack in areleased puller wire when the tip is deflected. The catheter may alsoinclude a pair of adjustable stops that are configured to stop theproximal ends of the puller wires from proximal movement beyond apredetermined stop location along the longitudinal axis. Fine, if notnearly infinitesimal, adjustment in the operating position of the pullerwires is accomplished by selectively adjusting the placement of thestops distally or proximally within the catheter housing.

In another embodiment, the control handle of the catheter includes adeflection knob that is rotationally coupled to the lever structurewhich enables the user to control deflection of the tip section with,preferably, a thumb and an index finger, when grasping the controlhandle. The catheter may also include a tension adjustment mechanism foradjusting the tightness of the deflection knob. In one embodiment, theadjustment mechanism includes a cap and a dial rotationally coupled toeach other, a friction nut, and a screw rotationally coupled to cap,whereby rotation of the dial selectively increases or decreases thefrictional bearing on the lever structure.

In yet another embodiment, the control handle of the catheter isoperational for deflection of the tip section without both housinghalves of the control handle being joined together. In that regard, thesteering assembly is configured to be operational when assembled withinone housing half not yet joined with the other housing half. A portformation enables the catheter body to be releasably held in the onehousing half such that the puller wires extending from the catheter bodycan be manipulated by the steering assembly so assembled.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a side view of an embodiment of the catheter of the invention.

FIG. 2 is a side cross-sectional view of the junction of the catheterbody and tip section of an embodiment of a catheter according to theinvention.

FIG. 3 is a transverse cross-sectional view of the catheter body shownin FIG. 2 taken along line 3-3.

FIG. 4 is a side cross-sectional view of the distal end of the tipsection shown in FIG. 2.

FIG. 5 is a transverse cross-sectional view of the tip section alongline 5-5.

FIG. 6 is a transverse cross-sectional view of a catheter tip sectionaccording to the invention where the puller wires are anchored to theside walls of the tip section.

FIG. 7 is a longitudinal cross-sectional view of a preferred puller wireT-bar anchor.

FIG. 8 is a longitudinal cross-sectional view of the puller wire T-baranchor of FIG. 7 rotated 90.degree. to show the cross-piece on end.

FIG. 9 is a top exploded view of a control handle of the catheter ofFIG. 1.

FIG. 10 is a view of a housing half of control handle and selectedcomponents of the steering assembly of the catheter of FIG. 1.

FIGS. 11 a and 11 b are views of a lever structure.

FIGS. 12 a-12 c show components of the steering assembly, respectively,as without deflection in the tip section of the catheter, withdeflection of the tip section to the right, and with deflection of thetip section to the left.

FIGS. 13 a and 13 b are views of different embodiments of a fastenerfastening a free end of an embodiment of a constant force spring to aproximal end of a puller wire.

FIGS. 14 a, 14 c and 14 e are perspective views of different embodimentsof a stop member.

FIGS. 14 b, 14 d and 14 f are cross-sectional views of the stop membersof FIGS. 14 a, 14 c and 14 e, respectively, as situated in a housinghalf of the control handle.

FIG. 15 is a view of a deflection knob.

FIG. 16 is a view of the housing half of FIG. 10 with parts broken awayand a friction nut.

FIG. 17. is a cross-sectional view of the control handle of the catheterof FIG. 9 taken generally along the axis 75 parts broken away.

FIG. 18. is a view of components of a tension adjustment assembly.

FIG. 19 is a view of a first housing half joined with a second housinghalf.

FIG. 20 is a view of a cap of the tension adjustment assembly.

FIG. 21 is a view of a finger dial of the tension adjustment assembly.

FIG. 22 is a view of a pulley.

FIG. 23 is a view of an embodiment of another housing half of thecontrol handle.

FIG. 24 is a cross sectional view taken along Lines W-W in FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

In an embodiment of the invention, there is provided a steerablebidirectional electrode catheter. As shown in FIG. 1, the catheter 10comprises an elongated catheter body 12 having proximal and distal ends,a tip section 14 at the distal end of the catheter body 12, and acontrol handle 16 at the proximal end of the catheter body 12.

As shown in FIGS. 2 and 3, the catheter body 12 comprises an elongatedtubular construction having a single axial or central lumen 18. Thecatheter body 12 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The catheter body 12 can be of anysuitable construction and made of any suitable material. A presentlypreferred construction comprises an outer wall 20 made of polyurethaneor PEBAX. The outer wall 20 preferably comprises an imbedded braidedmesh of stainless steel or the like to increase torsional stiffness ofthe catheter body 12 so that when the control handle 16 is rotated thetip section 14 will rotate in a corresponding manner.

The overall length and diameter of the catheter 10 may vary according tothe application. A presently preferred catheter 10 has an overall lengthof about 48 inches. The outer diameter of the catheter body 12 is notcritical, but is preferably no more than about 8 french. The innersurface of the outer wall 20 is preferably lined with a stiffening tube22, which can be made of any suitable material, preferably nylon orpolyimide. The stiffening tube 22, along with the braided outer wall 20,provides improved flexural and torsional stability while at the sametime minimizing the wall thickness of the catheter body 12, thusmaximizing the diameter of the central lumen 18. The outer diameter ofthe stiffening tube 22 is about the same as or slightly smaller than theinner diameter of the outer wall 20. A particularly preferred catheter10 has an outer diameter of about 0.092 inch and a lumen 18 diameter ofabout 0.052 inch.

As shown in FIGS. 4 and 5, the tip section 14 comprises a short sectionof flexible tubing 24 having a first off-axis lumen 26 and a secondoff-axis lumen 28. The flexible tubing 24 is made of a suitablenon-toxic material that is preferably more flexible than the catheterbody 20. A presently preferred material for the tubing 24 is braidedpolyurethane, i.e., polyurethane with an embedded mesh of braidedstainless steel or the like. The outer diameter of the tip section 14,like that of the catheter body 12, is preferably no greater than about 7french, more preferably about 6½ french or less.

The off-axis lumens 26, 28 extend through diametrically opposed halvesof the tip section 14. The off-axis lumens 26, 28 are asymmetrical andtherefore non-interchangeable. The first off-axis lumen 26 is smallerthan the second off-axis lumen 28. In an 8 french or 7 french diametercatheter, where the tip section is 6½ french, it is preferred that thefirst off-axis lumen 26 has a diameter ranging from about 0.018 inch toabout 0.025 inch, more preferably from about 0.018 inch to about 0.022inch. Preferably, the second off-axis lumen 28 has a diameter rangingfrom about 0.022 inch to about 0.030 inch, more preferably from about0.026 inch to about 0.028 inch.

By using two rather than three lumens along a single diameter, thepresent design retains the simplified construction of the unidirectionaldeflectable steerable catheter described in U.S. Pat. No. Re 34,502,which is incorporated herein by reference. However, it is understoodthat additional lumens may be provided in the tip section. As describedin U.S. Pat. No. 6,171,277, the disclosure of which is incorporatedherein by reference, the tip section 14 may contain four lumens, two ofwhich have a greater diameter of about 0.029 inch and two of which havea lesser diameter of about 0.018 inch. Lead wires for the electrodes,thermocouple wires and/or electromagnetic sensor cable may extendthrough different lumen(s) from those through which each of puller wiresextends. As such, the present invention may employ two or more lumens inthe tip section 14.

A preferred means for attaching the catheter body 12 to the tip section14 is illustrated in FIG. 2. The proximal end of the tip section 14comprises an outer circumferential notch 34 that receives the innersurface of the outer wall 20 of the catheter body 12. The tip section 14and catheter body 12 are attached by glue or the like. Before the tipsection 14 and catheter body 12 are attached, however, the stiffeningtube 22 is inserted into the catheter body 12. The distal end of thestiffening tube 22 is fixedly attached near the distal end of thecatheter body 12 by forming a glue joint with polyurethane glue or thelike. Preferably a small distance, e.g., about 3 mm, is provided betweenthe distal end of the catheter body 12 and the distal end of thestiffening tube 22 to permit room for the catheter body 12 to receivethe notch 34 of the tip section 14. A force is applied to the proximalend of the stiffening tube 22, and, while the stiffening tube 22 isunder compression, a first glue joint (not shown) is made between thestiffening tube 22 and the outer wall 20 by a fast drying glue, e.g.Super Glue®. Thereafter a second glue joint is formed between theproximal ends of the stiffening tube 22 and outer wall 20 using a slowerdrying but stronger glue, e.g., polyurethane.

A spacer 36 lies within the catheter body 12 between the distal end ofthe stiffening tube 22 and the proximal end of the tip section 14. Thespacer 36 is preferably made of a material that is stiffer than thematerial of the tip section 14, e.g., polyurethane, but not as stiff asthe material of the stiffening tube 22, e.g. polyimide. A spacer made ofTeflon® is presently preferred. A preferred spacer 36 has a length offrom about 0.25 inch to about 0.75 inch, more preferably about 0.50inch. Preferably the spacer 36 has an outer and inner diameter about thesame as the outer and inner diameters of the stiffening tube 22. Thespacer 36 provides a transition in flexibility at the junction of thecatheter body 12 and the tip section 14 to bend smoothly without foldingor kinking.

In the depicted embodiment, the distal end of the tip section 14 carriesa tip electrode 38 (see FIGS. 1 and 4). Mounted along the length of thetip section 14 is a ring electrode 40 (see FIG. 4). The length of thering electrode 40 is not critical, but is preferably about 1 mm to about3 mm. Additional ring electrodes can be provided if desired. If multiplering electrodes are used, they are spaced apart in any fashion asdesired so long as their edges do not touch.

As shown in FIGS. 2-5, the tip electrode 38 and ring electrode 40 areeach connected to a separate lead wire 30. Each lead wire 30 extendsthrough the second off-axis lumen 28 in the tip section 14 (FIG. 5),through the central lumen 18 in the catheter body 12 (FIG. 3) andthrough the control handle 16. The proximal end of each lead wire 30extends out the proximal end of the control handle 16 and is connectedto an appropriate connector, which can be plugged into or otherwiseconnected to a suitable monitor, source of energy, etc.

The lead wires 30 are connected to the tip electrode 38 and ringelectrode 40 by any conventional technique. Connection of a lead wire 30to the tip electrode 38 is preferably accomplished by solder or thelike. Connection of a lead wire 30 to the ring electrode 40 ispreferably accomplished by first making a small hole through the tubing24. Such a hole can be created, for example, by inserting a needlethrough the tubing 24 and heating the needle sufficiently to form apermanent hole. The lead wire 30 is then drawn through the hole by usinga microhook or the like. The end of the lead wire 30 is then stripped ofany coating and welded to the underside of the ring electrode 40, whichis then slid into position over the hole and fixed in place withpolyurethane glue or the like.

As also shown in FIGS. 2-5, two puller wires 32 extend through thecatheter 10. Each puller wire 32 extends from the control handle 16,through the central lumen 18 in the catheter body 12 (FIG. 3) and intoone of the off-axis lumens 26 and 28 of the tip section 14 (FIG. 5). Asdescribed in more detail below, proximal movement of the proximal end ofeach puller wire 32 is predeterminedly limited within the control handle16 and the distal end of each puller wire 32 is anchored within the tipsection 14.

Each puller wire 32 is made of any suitable metal, such as stainlesssteel or Nitinol. Preferably each puller wire 32 has a coating, such asa coating of Teflon® or the like. Each puller wire 32 has a diameterpreferably ranging from about 0.006 inch to about 0.0010 inch.Preferably both of the puller wires 32 have the same diameter.

Each puller wire 32 is anchored near the distal end of the tip section14. In the embodiment depicted in FIG. 4, the puller wires 32 are bothanchored to the tip electrode 38 by a welding or the like.

Alternatively, the puller wire 32 in the first off-axis lumen 26 can beanchored to the side wall of the tip section 14. As shown in FIGS. 7 to9, the puller wire 32 is preferably attached by means of an anchor 44fixedly attached to the distal end of the puller wire 32. The anchor 44is formed by a metal tube 45, e.g., a short segment of hypodermic stock,that is fixedly attached, e.g. by crimping, to the distal end of thepuller wire 32. The tube has a section that extends a short distancebeyond the distal end of the puller wire 32. A cross-piece 47 made of asmall section of stainless steel ribbon or the like is soldered orwelded in a transverse arrangement to the distal end of the metal tubewhich is flattened during the operation. This creates a T-bar anchor 44.A notch is created in the side of the tip section 14 resulting in anopening in the off-axis lumen 26 carrying the puller wire 32. The crosspiece 47 lies transversely within the notch. Because the length of theribbon forming the cross-piece 47 is longer than the diameter of theopening into the off-axis lumen 26, the anchor 44 cannot be pulledcompletely into the off-axis lumen 26. The notch is then sealed withpolyurethane glue or the like to give a smooth outer surface. The glueflows into the off-axis lumen 26 to fully secure the anchor. A tunnel,in the form of polyimide tubing or the like, can be provided to permitpassage of the lead wire 30 through the glue so that this same pullerwire anchor construction can be used in the second off-axis lumen 28.Other means for anchoring the puller wires 32 in the tip section 14would be recognized by those skilled in the art and are included withinthe scope of the invention.

Referring back to FIGS. 1 and 2, the catheter 10 further comprises twocompression coils 46, each in surrounding relation to a correspondingpuller wire 32. Each compression coil 46 is made of any suitable metal,such as stainless steel. Each compression coil 46 is tightly wound onitself to provide flexibility, i.e., bending, but to resist compression.The inner diameter of each compression coil 46 is slightly larger thanthe diameter of its associated puller wire 32. For example, when apuller wire 32 has a diameter of about 0.007 inch, the correspondingcompression coil 46 preferably has an inner diameter of about 0.008inch. The coating on the puller wires 32 allows them to slide freelywithin the compression coil 46. The outer surface of each compressioncoil 46 is covered along most of its length by a flexible,non-conductive sheath 48 to prevent contact between the compression coil46 and the lead wires 30 within the central lumen 18. The non-conductivesheath 48 made of thin-walled polyimide tubing is presently preferred.

As shown in FIG. 2, at the distal end of the catheter body, the twocompression coils 46 are positioned in diametric opposition within thestiffening tube 22 and spacer 36 so that they can be aligned with thetwo off-axis lumens 26,28 in the tip section 14. The compression coils46 and stiffening tube 22 are sized so that the compression coils 46 fitclosely and slidably within the stiffening tube 22. With this design,the lead wires 30 distribute themselves around the two compression coils46 without misaligning the coils.

The compression coils 46 are secured within the catheter body 12 withpolyurethane glue or the like. Each compression coil 46 is anchored atits proximal end to the proximal end of the stiffening tube 22 in thecatheter body 12 by a glue joint (not shown). When a stiffening tube 22is not used, each compression coil is anchored directly to the outerwall 20 of the catheter body 12.

Still referring to FIG. 2, the distal end of each compression coil 46 isanchored to the distal end of the stiffening tube 22 in the catheterbody 12 by a glue joint 52, or directly to the distal end of the outerwall 20 of the catheter body 12 when no stiffening tube 22 is used.Alternatively, the distal ends of the compression coils 46 may extendinto the off-axis lumens 26, 28 of the tip section 14 and are anchoredat their distal ends to the proximal end of the tip section 14 by a gluejoint. In the depicted embodiment, where the compression coils 46 areeach surrounded by the sheath 48, care should be taken to insure thatthe sheath is reliably glued to the compression coil. The lead wires 30can also be anchored in the glue joint. However, if desired, tunnels inthe form of plastic tubing or the like can be provided around the leadwires at the glue joint to permit the lead wires to be slidable withinthe glue joint.

Both glue joints preferably comprise polyurethane glue or the like. Theglue may be applied by means of a syringe or the like through a holemade between the outer surface of the catheter body 20 and the centrallumen 18. Such a hole may be formed, for example, by a needle or thelike that punctures the outer wall 18 and the stiffening tube 22 that isheated sufficiently to form a permanent hole. The glue is thenintroduced through the hole to the outer surface of the compression coil46 and wicks around the outer circumference to form a glue joint aboutthe entire circumference of each sheath 48 surrounding each compressioncoil 46. Care must be taken to insure that glue does not wick over theend of the coil so that the puller wire cannot slide within the coil.

As best shown in FIGS. 2 and 5, within the off-axis lumens 26, 28, eachpuller wire 32 is surrounded by a plastic sheath 42, preferably made ofTeflon®. The plastic sheaths 42 prevent the puller wires 32 from cuttinginto the wall of the tip section 14 when the tip section is deflected.Each sheath 42 ends near the distal end of each puller wire 32.Alternatively, each puller wire 32 can be surrounded by a compressioncoil where the turns are expanded longitudinally, relative to thecompression coils extending through the catheter body, such that thesurrounding compression coil is both bendable and compressible.

Longitudinal movement of the puller wires 32 relative to the catheterbody 12, which results in deflection of the tip section 14, isaccomplished by manipulation of the control handle 16. A suitablebidirectional control handle for use in the present invention isillustrated in FIGS. 9-24.

As shown in FIGS. 9 and 10, the control handle 16 comprises a generallyelongated handle housing 60, which can be made of any suitable rigidmaterial. The housing 60 can be of a unitary construction or of twoopposing halves 64, 66 that are joined by glue, sonic welding or othersuitable means along a longitudinal peripheral seam 59 around thehousing. The control handle 16 comprises a steering assembly 68 thatcontrols deflection of the tip section 14 in response to manipulationsby the user. The steering assembly comprises a lever structure 70 havinga pair of coordinated pulleys 72 that act on the puller wires to deflectthe tip section, a pair of constant force springs 74 that are attachedto the proximal ends of the puller wires, and a pair of adjustable stops76 which prevent the proximal ends of the puller wires from movingproximally past a selected stop position within the control handle 16.The steering assembly 68 is advantageously configured to provide arelatively shorter angular throw while increasing, if not at leastgenerally doubling, the throw capacity of the catheter. In particular,the steering assembly has a minimized moment of inertia about its throwaxis 75, while generally doubling the travel distance of a puller wirein relation to the travel distance of the respective pulley drawing thatpuller wire, despite the relatively small interior of the housing.Moreover, the steering assembly provides a minimal angle between alongitudinal axis 77 of the control handle 16 and a segment of thepuller wire drawn to accomplish deflection, for more efficient use ofthe force applied by the user in operating the control handle.

As better shown in FIGS. 10, 11 a and 11 b, the lever structure 70 issomewhat elongated along an axis 84, having a wider center portion 78between two narrower end portions 80. To deflect the tip section of thecatheter, the lever structure is rotatable at its center about the throwaxis 75, which is generally perpendicular to the longitudinal axis 77 ofthe control handle 16. A neutral position along axis 79 is defined forthe lever structure when its longitudinal axis 84 is generallyperpendicular to the longitudinal axis 77 of the control handle 16. Thelever structure is rotatable from its neutral position in the clockwisedirection by angle +α and in the counterclockwise direction by angle −α.The end portions 80 are configured with apertures 86, at a radialdistance R from the throw axis 75, in which the pulleys 72 (of whichonly one is illustrated in FIGS. 10, 11 a and 11 b) are situated. Asshown in FIGS. 12 a-12 c, with rotation of the lever structure 70, onepulley 72 is translated distally as the other pulley 72 is translatedproximally. Moreover, the lever structure and the pulley are configuredsuch that each pulley can rotate counterclockwise or clockwise withinits aperture about its own axis. To that end, each pulley has a core 73(FIG. 22) about which a puller wire is trained.

Referring more to FIG. 10, the housing 60 is configured at its distalend with a port 90 through which the puller wires (now designated as 32a and 32 b for more clarify) enter the control handle 16. In the housinghalf 66 that is shown in FIG. 10, a divider 92 is configured in theinner surface and proximal of the port to extend linearly between theport and the lever structure 70. A distal end 94 of the divider istapered to define diverging puller wire pathways from the port toward arespective pulley 72 in the lever structure. For ease of discussion, thehousing half 66 may be described as divisible along the divider 92 intotop and bottom housing quarters 96 a, 96 b, which are more or lessmirror counterparts of each other in terms of physical layout andoperation. Accordingly, the following description uses similar referencenumerals for similar structures except the numerals are followed by theletter a or the letter b.

The top housing quarter 96 a is configured with a rail 100 a thatextends parallel with the divider 92. The rail and an adjacent side 102a of the housing 60 define a channel 104 a that extends between thepulley 72 a and the distal end of the housing quarter which isconfigured with a well 106 a that is in communication with the channel.Fixedly situated in the well is the spring 74 a whose free end 109 aextends proximally into the channel. Releasably and hence adjustablymounted onto the rail 100 a is the stop 76 a.

Correspondingly, the bottom housing quarter 96 b is configured with arail 100 b that extends parallel with the divider 92. The rail and anadjacent side 102 b of the housing define a channel 104 b that extendsbetween the pulley 72 b (not shown) and the distal end of the housingquarter which is configured with a well 106 b that is in communicationwith the channel. Fixedly situated in the well is the spring 74 b whoseactive end 109 b extends proximally into the channel. Releasably andhence adjustably mounted onto the rail 100 b is the stop 76 b.

The inner surface of the housing half 64 has formations in structuralcorrespondence with the aforementioned formations of the housing half66. Accordingly, as shown in FIG. 23, the inner surface is formed with acounterpart divider 93, counterpart rails 101, counterpart sides 103,and counterpart wells 107.

In view of the foregoing, the travel path within the housing of eachpuller wires is as follows: a first generally linear path, a non-linear(including, e.g., a U-turn or doubling back) path, and a secondgenerally linear path, each leg of which is described below in furtherdetail.

Referring to FIGS. 10 and 12 a, the puller wire 32 a, whose distal endis affixed to the tip section 14, enter the control handle 16 in aproximal direction via the port 90. At the tapered distal end 94 of thedivider 92, the puller wire 32 a diverges from the puller wire 32 b andcontinues proximally in a minimally diagonal direction toward the pulley72 a in the lever structure 70. This section of the travel path, asdefined between the tapered end 94 and the pulley 72 a, is generallylinear. This linear segment of the puller wire 32 a is hereinaftergenerally referred to by the numeral 108 a (FIG. 12 a).

The puller wire 32 a then enters the lever structure 70 proximallythrough a slit opening 110 (best seen in FIG. 11 a) on the distal sideof the lever structure and is trained counterclockwise about the pulley72 a before exiting the lever structure distally through the same slitopening. The puller wire is trained about the pulley for a predetermineddegree ranging between about 172-195, preferably 177-190, or morepreferably about 180-187. As such, the travel path of the puller wire 32also includes a section having a U-turn or a doubling-back at thepulley. This nonlinear segment of the puller wire is designated by thenumeral 111 a (FIG. 12 a).

The puller wire 32 a then veers inwardly and continues generallydistally to enter the channel 104, which defines yet another section ofthe travel path. Within the channel, the proximal end of the puller wire(so designated despite its being physically distal of a precedingsegment) is attached to the free end 109 a of the spring 74 a. Thelinear segment of this travel path is designated by the numeral 112 a(FIG. 12 a).

Correspondingly, the puller wire 32 b travels a similar path having afirst linear segment 108 b, followed by a nonlinear segment 111 b andfurther followed by a second linear segment 112 b, except that thesegment 111 b is trained clockwise on the pulley 72 b. Moreover, theproximal end of the puller wire 32 b (so designated despite its beingphysically distal of a preceding segment) is attached to the free end109 b of the spring 74 b (not visible in FIG. 10).

In the disclosed embodiment, the constant force springs 74 a, 74 b areflat coil springs as best seen in FIG. 10. Each spring member exerts aforce in the distal direction ranging between about 0.50 ounces and 9.0ounces, and preferably of about 1.0 ounce. As shown in FIGS. 13 a and 13b, free ends 109 a, 109 b of the springs 74 a, 74 b are attached to theproximal ends of the puller wires 32 a, 32 b by a fastener 111, e.g., acrimp fastener 113 (FIG. 13 a), a welded joint 114 (FIG. 13 b).

Configured to act on the free ends 109 are the stops 76 which limitextension of the ends 109 in the proximal direction (and hence proximalmovement of the proximal ends of the puller wires 32) past apredetermined stop location along the rails 100. Accordingly, each stop76 a, 76 b is positioned proximally of the respective free end 109and/or fastener 111. As shown in FIGS. 14 a and 14 b, each stop cancomprise a generally U-shaped spring clip member 76 i (e.g., constructedfrom a shaped piece of sheet metal) having a base 116 and legs 118 thatreleasably straddle the rail. The member 76 i is shaped such that one ofits legs 118 sits deep in the channel 104 and projects minimally intothe channel so as to avoid interfering with the distal or proximalmovement of the puller wires 32 but sufficiently to stop the free ends109 of the springs or the fastener 111 from passing proximally.

As shown in FIGS. 14 c-14 d, each stop can also comprise a generallyS-shaped spring clip member 76 j (e.g., constructed from a piece ofshaped sheet metal) which has a first arm 117 that wraps around eitherthe rail 100 or the side 102 and a second arm 119 that sits deep in thechannel 104 to adjustably anchor the member 76 j to the rail 100, theside 102 and/or in the channel 104. Again, the member 76 j has a profilethat projects minimally into the channel 104, but sufficiently so as toblock the free ends 109 of the springs 74 or the puller wire fasteningmeans from passing proximally.

Each stop can further comprise a hollow elongated member 76 k (e.g., acylinder formed from a rolled piece of sheet metal) whose an interiorspace or volume along the length is generally constant until at itsproximal end 121 which can flare when the circumference is unrestrained.A corresponding, thus close-fitting tubular cross section 123 isprovided in facing surfaces of the rail 100 and the side 102 such thatthe member 76 k can slide or move distally within the channel 104 but isgenerally restricted against proximal movement by the frictionalengagement of the flared proximal end 121 against the rail and the wallwithin the cross section 123. It is understood that the configuration orform of the stops 76 a, 76 b is limited by only its function and purposeto adjustable set a stop position and the stops may therefore take onother forms not expressly described herein.

It can be seen from FIGS. 12 a-12 c. that rotation of the leverstructure 70 causes deflection in the catheter tip section 14. That is,when the lever structure is rotated in the clockwise rotation (namely,in the +α direction) (FIG. 12 b), the pulley 72 a is translatedproximally. Because the puller wire 32 a trained on the pulley 72 a isstopped against proximal movement at its proximal end by the stop 76 a,the proximal translation of the pulley 72 a causes it to rotatecounterclockwise thereby drawing proximally the wire segment 108 a,which results in deflection of the tip section 14 to the right.Facilitating this deflection is the release of the segment 112 b as thepulley 72 b is coincidentally translated distally by the lever structure70. The resulting slack in the segment 112 b is taken up by the spring74 b as the pulley 72 b rotates clockwise.

Correspondingly, when the lever structure is rotated in thecounterclockwise rotation (namely, in the −α direction) (FIG. 12 c), thepulley 72 b is translated proximally. Because the puller wire 32 btrained on the pulley 72 b is stopped against proximal movement at itsproximal end by the stop 76 b, the proximal translation of the pulley 72b causes it to rotate clockwise thereby drawing proximally the wiresegment 112 b, which results in deflection of the tip section 14 to theleft. Facilitating this deflection is the release of the segment 112 aas the pulley 72 a is coincidentally translated distally by the leverstructure 70. The resulting slack in the segment 112 a is taken up bythe spring 74 a as the pulley 72 a rotates counterclockwise.

Although each of the actuating pulley has translated proximally only adistance x (FIGS. 12 b and 12 c) along the longitudinal axis 75 as aresult of the rotation of the lever structure 70, the length of thepuller wire drawn by that pulley proximally from the port in deflectingthe tip section is about 2×. Consequently, the present inventionprovides a catheter with nearly double the throw in tip deflection,despite the small interior space of the control handle.

Because of the repeated cycles of bending each puller wire canexperience around its pulley, the proximal segment(s) of each pullerwithin the control handle may comprise a flexible braided cable and/orKevlar® rope which can better withstand such stress and strain. To thatend, the cable or rope has a length of at least 2×, with a portionthereof trained around the pulley. Its distal and proximal ends may beattached to the puller wire and the spring, respectively, by crimpfasteners. Accordingly, it is understood that the proximal end of thepuller wire and the proximal end of the cable or rope are usedinterchangeably herein as appropriate.

Also in accordance with the present invention, as shown in FIGS. 12 a-12c, an angle of alignment of the segments 108 a, 108 b deviates onlyminimally from the longitudinal axis 77 which provides greater operatingefficiency in the force required to deflection the tip section 14. Inthe disclosed embodiment, a deviation angle θ may range between about 5to 12 degrees, preferably between 6 and 10 degrees and more preferablybetween 7 and 8 degrees, when the lever structure is in the neutralposition (namely, when α is at or near 0) (FIG. 12 a). Because thepulleys 72 each travel a circular path when translated by the leverstructure 70, the angle θ can be further decreased by up to about 2-4degrees (that is, decreases down to about θ=3) during this translation(FIGS. 12 b and 12 c). In any case, given such a minimal range of angleθ, most of the force that is applied to draw a puller wire proximallyalong the longitudinal axis 77 for deflecting the tip section in thedirection of the off axis lumen in which that puller wire extends isadvantageously met by the proximal translation of the pulley drawingthat puller wire along the angle θ.

In accordance with the present invention, an initial neutral position(with little or no detectable deflection) (FIG. 12 a) in the tip section14 can be readily calibrated by selective placement of each of the stops76 a, 76 b distally or proximally along the rails 100 a, 100 b. With thelever structure 70 resting in a neutral position, the operating positionof each puller wire 32 can be adjusted so that it is sufficiently tautin drawing the ends 109 of the springs 74 against the stops 76 withoutcausing any detectable deflection in the tip section 14. As describedabove in relation to FIGS. 11-13, the stop location of each stop 76 a,76 b determines how much distance the corresponding pulley needs to bemoved (or the corresponding puller wire needs to travel) proximallybefore the tip section 14 begins to deflect in that direction. In thatregard, it is understood that the puller wires can also be adjusted toprovide the catheter with a predetermined amount of free play in theneutral position so that the catheter body and/or elements surroundingthe puller wires (e.g., the outer wall 20 and/or the stiffening tube 22)can shrink or stretch, such as during sterilization of the catheter,without adversely deforming the puller wires. In accordance with thepresent invention, fine, if not near infinitesimal, adjustment of a stopposition for each puller wire is enabled in the control handle 16. Assuch, these adjustments of the stop position of each puller wire canalso be used to compensate for certain characteristics in the catheter,including puller wires with unequal actual lengths and/or counterpartcomponents in the steering assembly or the control handle that are notexact duplicates of each other in terms of size or operatingcharacteristics. Stop adjustments should be performed to attain aneutral position with little or no detectable deflection in the cathetertip section 14 before the housing halves 64, 66 are joined to eachother.

Referring back to FIG. 9, the lever structure 70 of the steeringassembly 68 is enclosed within the housing halves 64, 66 and ismanipulated from outside the housing by a deflection knob 128.Deflection of the catheter 10 can therefore be comfortably controlledby, preferably, the thumb and/or index finger of the user when graspingthe control handle 16. Rotation of the deflection knob about the throwaxis 75 is directly coupled to rotation of the lever structure 70primarily by means of an annular protrusion 130 (FIGS. 10 and 11 b)formed in the lever structure. The protrusion 130 is centered about anaperture 132 aligned with the throw axis 75 and extends in the directionof the deflection knob 128. The protrusion 130 has two recesses 134aligned along a diameter which allows the lever structure to lock inalignment with the deflection knob. The protrusion also has a dimensionalong the throw axis 75 that enables the protrusion to extend throughand beyond an aperture 136 in the housing half 64 (FIG. 23) to reach afacing surface 138 of the deflection knob 128 (FIG. 15). The facingsurface 138 is formed with counterpart annular recess 140 and similarlyaligned protrusions 142 that match, respectively, the annular protrusion130 and aligned recesses 134 of the lever structure 70. These matchingformations are sized such that the deflection knob can be frictionallyor snap-fitted (and secure by glue if appropriate) through the aperture136 the housing half 64 onto the protrusion 130 of the lever structure.In this manner, the deflection knob 128 and the lever structure 70 arejoined to the housing half 64 yet coupled for joint rotation relative tothe housing half 64 about the throw axis 75. Consequently, clockwiserotation of the deflection knob causes clockwise rotation of the leverstructure, and counter-clockwise rotation of the deflection knob causescounterclockwise rotation of the lever structure. In the disclosedembodiment, the recesses 134, 140 and protrusions 130, 142 are alsoconveniently aligned with arms 144 (FIG. 15) of the deflection knob soas to give the user a visual indication of the rotational position ororientation of the lever structure 70.

Because the deflection knob 128 and the lever structure 70 arerotational coupled, rotation of the deflection knob may also bedescribed in terms of the aforementioned angle α. As illustrated inFIGS. 12 a-12 c, the range of angle α is predetermined primarily by thearcuate profile of the housing near the throw axis 75. Concave orgenerally recessed sections 150 (see also FIG. 10) of the housing halves64, 66 abut with the arms 144 of the deflection knob thus preventingfurther clockwise rotation beyond the angle +α (FIG. 12 b) andcounterclockwise rotation beyond the angle −α (FIG. 12 c). It isunderstood that the range of rotation of the deflection knob 128 can bevaried by altering the profile or curvature of the sections 150.Moreover, the sections 150 on each side of the neutral position of thelever structure 70 need not be identical; a greater counterclockwiserotation angle and/or a lesser clockwise rotation angle are possible,and vice versa.

In the disclosed embodiment, the angle α of the lever structure 70 (andhence the deflection knob 128) ranges between about 0 and 70 degrees,preferably between about 30 and 60 degrees and more preferably betweenabout 40 to 50 degrees. Accordingly, the disclosed embodiment provides atotal range of rotation (from −α to +α) of between about 0 and 140degrees, preferably between about 60 and 120 degrees and more preferablybetween about 80 to 100 degrees.

Significantly, the control handle 16 is configured such that it need notbe fully assembled for the steering assembly 68 and deflection of thetip section 14 to be effectively tested and evaluated. In particular,the steering assembly 68 can be tested and evaluated when assembledsolely within the housing half 66 and operated on by the deflection knob128 mounted onto the lever structure without the housing half 64. Tothat end, the housing half 66 is configured at or near the port 90 witha formation 91 (FIG. 24) that releasably holds the proximal end of thecatheter body 12 (whose outer wall 20 and stiffening tube 22 generallyterminate proximal of the formation 91 so that the pulley wires 32 andcan extend freely and uncovered into the control handle 16). Theformation can include a pair of tabs 93 defining a space in which thecatheter body can be snapped into and releasably held to facilitate thetesting and evaluation of the deflection operation of control handlewithout the housing half 64.

In the assembly of the remainder of the control handle, reference ismade to FIGS. 9, 11 a, and 16-21. A second annular protrusion 152 on asurface 154 of the lever structure 70 facing the housing half 66 isreceived in an annular indentation 156 (FIG. 19) formed in the housinghalf 66. The annular indentation 156 of the housing half 66 isconcentric with an aperture 158 that is aligned with the throw axis 75and has a geometric (non-circular) or hexagonal cross-section. In theillustrated embodiment, the control handle 16 includes a tensionadjustment mechanism 160 (FIG. 9) that is mounted onto the outside ofthe housing half 66. The mechanism 160 which can be manipulated toadjust the tightness or tension of the rotational movement of deflectionknob 128 includes a cap 162 and a finger dial 164 that are rotationallycoupled, a friction screw 166 that is rotationally coupled to the cap,and a friction nut 167 that is in engagement with the friction screw166.

As best shown in FIG. 17, the friction nut 167 is situated in theaperture 132 of the lever structure 70. The friction nut is configuredwith a lip 176 at one end that engages with a corresponding diameter 178in the aperture 132 of the lever structure 70. The lip 176 and thediameter 178 are oriented such that they point toward the deflectionknob 128. On an end face of the lip, there are two recesses on adiameter of the outer surface of the lip 179 which can receive the headof a screwdriver that may be used during assembly of the control handle16. At an end 169 of the nut 167, it is provided with a geometric orhexagonal cross section 177 that matches the aperture 158 of the housinghalf 66. The length of the nut 167 allows the end 169 to be received inthe aperture 158 so that the nut is secured with the housing half 66against rotation about the throw axis 75.

An inner surface 168 of the cap 162 (FIG. 18) facing the outside of thehousing half 66 defines a raised circular portion 170 that fits within acorresponding indented circular portion 172 (FIG. 19) in the outer faceof the housing half 64. With a central aperture 174 (FIG. 18) of the capconcentric with the hexagonal aperture 158 (FIG. 19) which leads to athreaded interior of the friction nut 167 (FIG. 17) within the leverstructure 70, the screw 166 (not shown in FIG. 17, but shown in FIG. 9)is inserted through the aperture 174 and the aperture 158 and its endadvanced into threaded engagement with the end 169 of the friction nut167. As shown in FIG. 20, the aperture 174 has three depths when viewedfrom its outside surface. A first depth has a smaller circular crosssection 180 defining a passage for the screw 166 completely through thecap 162. A second depth has a geometric or hexagonal cross section 182about mid-depth so as to anchor a geometric or hexagonal screw head 184(FIG. 9) against axial movement toward the friction nut 167 and torotationally couple the cap 162 and the screw 166 to each other. A thirddepth 186 has a larger circular cross section whose depth sufficientlyenables the cap to receive a facing circular portion 188 of the fingerdial 164 (FIG. 22).

Referring to FIGS. 19-21, covering the screw head 184, the finger dial164 is mounted outside of the cap 162 by prongs 190 (FIG. 21) thatprotrude from the finger dial in opposing positions across the portion188, for frictional snug fitting into (and beyond) apertures 192 (FIGS.18, 20) form on a diameter of the cap 162. And, because the cap 162 andthe finger dial 164 have rotational freedom relative to the housing half66, the outside surface 194 of the housing half 66 is configured withtwo curved recesses 196 (FIG. 19) which not only accommodate rotationmovement of the ends of the prongs 190 extending past the cap, buteffectively limit such rotational movement about the throw axis 75 toabout 60 degrees, preferably about 50 degrees, or more preferably about45 degrees. Accordingly, when the finger dial 164 is rotated, the cap162 (rotationally coupled thereto by the prongs 190) and the screw 166(rotationally coupled to the cap 162 by the hexagonal head 184) arejointly rotated.

Where the dial 167 is rotated to advance the screw 166 into the frictionnut, the friction nut 167 is drawn toward the adjustment mechanism 160thereby drawing the lever structure 70 toward the inside of the housinghalf 66 to increase the frictional contact or bearing between the secondannular protrusion 152 of the lever structure 70 against the indentedcircular portion 172 of the inner surface of housing half 66. Thetension of the lever structure 70 and hence the deflection knob 128against rotational movement is thereby increased. Correspondingly, wherethe dial 164 is rotated to draw the screw 166 out of the friction nut167, the bearing of the protrusion 152 of the lever structure 70 againstthe portion 172 of the housing half 66 is decreased thereby decreasingthe tension of the lever structure 70 and the deflection knob 128against rotation. This bearing between the lever structure 70 and thehousing half 66, which can affect whether the deflection knob is at allrotatable, how much force the user is to apply in deflecting the tipsection and whether and/or how quickly the tip section can straightenafter deflection when the deflection knob is released, can therefore betightened or loosen as desired by the user in operating the deflectionknob 128.

In other embodiments, one or more additional off axis lumens may beprovided through which additional components, e.g., infusion tube, opticfiber, etc., may extend. Depending on the intended use of the catheter10, it can further comprise additional features such as temperaturesensing means, an optic fiber, an infusion tube, and/or anelectromagnetic sensor. Additionally, smaller components, such as atemperature sensing means, could also extend through the second lumen inthe tip section along with the puller wire and lead wire(s).

In the embodiments described above, the central lumen 18 of the catheterbody 12 is used for passage of the electrode lead wires 30 as well asthe two puller wires 32, compression coils 46 and, if present,thermocouple wires, electromagnetic sensor cable, optic fiber orinfusion tube. It is understood that the catheter body 12 couldalternatively comprise a plurality of lumens. However, the singlecentral lumen 18 is preferred because it has been found that a singlelumen body permits better control when rotating the catheter 10. Thesingle central lumen 18 permits the puller wires 32, compression coils46 and lead wires 30 to float freely within the catheter body 12. Ifsuch wires are restricted within multiple lumens, they tend to build upenergy when the control handle 16 is rotated, resulting in the catheterbody 12 having a tendency to rotate back if, for example, the handle 16is released, or if bent around a curve, to flip over, either of whichare undesirable performance characteristics.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention.

Accordingly, the foregoing description should not be read as pertainingonly to the precise structures described and illustrated in theaccompanying drawings, but rather should be read consistent with and assupport to the following claims which are to have their fullest and fairscope.

What is claimed is:
 1. A bi-directional catheter comprising: anelongated catheter body having proximal and distal ends; a catheter tipsection at the distal end of the catheter body and having first andsecond diametrically-opposed off-axis lumens; a control handle at theproximal end of the catheter body, the control handle having a housingcomprising two housing members that can be joined to enclose a steeringassembly; first and second puller wires configured to deflect the tipsection in response to the steering assembly; the steering assemblycomprising: a lever structure rotatable about an axis substantiallyperpendicular to a longitudinal axis of the control handle, the steeringassembly including at least two pulleys rotatably mounted on opposingportions of the lever structure, wherein the first puller wire extendsinto the first lumen in the tip section and the second puller wireextends into the second lumen in the tip section, and wherein a distalend of each of the first and second puller wires is anchored to the tipsection, wherein each of the first and second puller wires is trained ona respective pulley and rotation of the lever structure results inproximal movement of one of said pulleys relative to the control handlethereby drawing proximally at least a segment of its respective first orsecond puller wire for deflecting the tip section in the direction ofthe off-axis lumen in which that first or second puller wire extends,and wherein a travel path of each of the first and second puller wireswithin the housing comprises a first generally linear path, a secondgenerally non-linear path, and a third generally linear path; whereinthe steering assembly is operational on the puller wires to deflect thepuller wires without the housing members being joined.
 2. Abi-directional catheter of claim 1, wherein each of the first and secondpuller wires is trained about its respective pulley for at least about180 degrees.
 3. A bi-directional catheter of claim 1, wherein each ofthe first and second puller wires extends from a distal end of thecontrol handle to its respective pulley at an angle of no greater thanabout 10 degrees from the longitudinal axis of the control handle.
 4. Abi-directional catheter of claim 1, wherein each of the first and secondpuller wires extends from a distal end of the control handle to itsrespective pulley at an angle ranging between about 3 and 10 degreesfrom the longitudinal axis of the control handle.
 5. A bi-directionalcatheter of claim 1, wherein the control handle further comprises adeflection knob, wherein the deflection knob and the lever structure arerotationally coupled to each other.
 6. A bi-directional catheter ofclaim 5, further comprising an adjustment knob configured to adjusttension of the deflection knob.
 7. A bi-directional catheter of claim 6,wherein the adjustment knob comprises a dial.
 8. A bi-directionalcatheter of claim 7, wherein the adjustment knob further comprises amember configured to draw the lever structure toward the housing inresponse to rotation of the dial.
 9. A bi-directional catheter of claim1, further comprising: first and second constant force springs; a firststop positioned proximal a first connection between the first constantforce spring and a proximal end of the first puller wire; a second stoppositioned proximal a second connection between the second constantforce spring and a proximal end of the second puller wire.
 10. Abi-directional catheter of claim 9, wherein the first and second stopsprevent the proximal ends of the first and second puller wires frommoving proximally beyond a respective threshold location along thelongitudinal axis of the control handle.
 11. A bi-directional catheterof claim 1, wherein the constant force springs are positioned distal ofthe pulleys.
 12. A bi-directional catheter of claim 1, furthercomprising a divider extending along the longitudinal axis of thecontrol handle, said divider directing the first and second puller wiresat a threshold angle toward their respective pulleys.
 13. Abi-directional catheter of claim 1, wherein the lever structure rotateswithin a threshold range of angles from the axis substantiallyperpendicular to the longitudinal axis of the control handle.
 14. Abi-directional catheter of claim 13, wherein the threshold range isdependent on a profile of the control handle.
 15. A bi-directionalcatheter of claim 13, wherein the threshold range is about −50 to +50degrees.
 16. A bi-directional catheter comprising: an elongated catheterbody having proximal and distal ends; a catheter tip section at thedistal end of the catheter body comprising first and seconddiametrically-opposed off-axis lumens; a control handle at the proximalend of the catheter body, the control handle having a longitudinal axisand comprising at least a steering mechanism having a lever structurerotatable about an axis substantially perpendicular to the longitudinalaxis, the steering mechanism further including at least two pulleysrotatably mounted on opposing portions of the lever structure, thecontrol handle having two housing members that can be joined to enclosethe steering assembly; first and second puller wires, each of the firstand second puller wires having proximal and distal ends and extendingfrom the control handle through the catheter body, wherein the firstpuller wire extends into the first diametrically-opposed off-axis lumenin the tip section and the second puller wire extends into the seconddiametrically-opposed off-axis lumen in the tip section, and wherein thedistal end of each of the first and second puller wires is anchored tothe tip section, and wherein a travel path of each of the first andsecond puller wires within the control handle includes a first generallylinear path, a second generally non-linear path including a U-turn of atleast 180 degrees about a respective pulley, and a third generallylinear path; wherein rotation of the lever structure results in movementof one of said pulleys relative to the control handle thereby drawing atleast a segment of its respective first or second puller wire fordeflecting the tip section in the direction of the diametrically-opposedoff-axis lumen in which that first or second puller wire extends; andwherein the steering assembly is operational on the first and secondpuller wires to deflect the first and second puller wires without thehousing members being joined.
 17. A bi-directional catheter of claim 16,wherein the proximal end of each of the first and second puller wires isconnected to a constant force spring.
 18. A bi-directional catheter ofclaim 16, wherein a travel distance of a segment of one of the first orsecond puller wires drawn by its respective pulley for deflection isabout twice the travel distance of that pulley.
 19. A bi-directionalcatheter of claim 16, wherein a segment of one of the first or secondpuller wires drawn by its respective pulley for deflection extends at anangle of less than about 7 degrees from the longitudinal axis of thecontrol handle.